Prior art techniques for the manufacture of cigarette filters containing additive material by processing of continuous tow have involved the compression of rod-shaped tow to form a depression therein suited for the receipt of additive material. Typically, the tow is processed by long-known apparatus into rod configuration and tow compressing apparatus operates upon longitudinally spaced portions of the continuously advanced tow rod. Upon application of the additive material to the rod depressions, the rod is suitably closed about the material and further operated upon by wrapping, sealing and cutting units to form finished cigarette filters. Such prior art practices are set forth in U.S. Pat. Nos. 3,837,264, 3,844,200, 3,884,741, 3,910,166 and 3,847,064.
The above-discussed technique has advantage in various respects over other known practices in which individual filter plugs are separated from one another by spaces for receipt of additive material, such practice being generally referred to as plug-space-plug filter making. Thus, the first-discussed practice avoids the need for pre-forming individual filter plugs and maintaining precise spacing therebetween in the course of conveyance to additive material dispensing units. A disadvantage exists, however, in the first-discussed practice based on its characteristic tow compression. By reason thereof, the filament density per unit volume of the tow longitudinally of the finished filter element changes from nominal density in filter element portions not containing additive material, i.e., uncompressed regions, to undesirably increased density in those filter element portions corresponding to tow compression regions. Possible results are an undesirable increase of draw resistance in the vicinity of the additive material and undesired increase in plug firmness or in rod diameter in such filter portions.
It is an object of the present invention to provide improved cigarette filters containing additive material and improved methods and apparatus for processing of continuous filter tow to produce such filters.
It is a more general object of the invention to provide elongate articles, comprised of a plurality of continuous filaments and characterized by longitudinal variation in filamentary material volume accompanied by substantially constant filament density per unit volume throughout their longitudinal extent, and methods and apparatus for making the same.
In attaining the foregoing and other objects, the invention provides a practice whereby elongate filamentary material is advanced continuously longitudinally between mutually spaced issue and take-up locations and wherein longitudinally spaced extents of such material in transit between the locations are subjected to stretching while other extents of such material in transit are maintained in unstretched condition throughout such transit. The respective extents of the stretched and unstretched filamentary material extents are preselectable, whereby any desired longitudinal extent of lessened filamentary material volume may be provided in such continuously advancing tow while filament density per unit cross-section is maintained substantially constant.
In cigarette filter manufacture in accordance with the invention, low filament volume portions of the tow are selected in longitudinal extent corresponding to the extent of filter elements in which additive material is to be included. Accordingly, resistance to draw is generally uniform throughout the finished filter element and the additive material does not give rise to increased rod firmness or diameter.
The foregoing and other objects and features of the invention will be evident from the following detailed description of preferred practices and embodiments and from the drawings wherein like reference numerals identify like parts throughout.